The ability to redirect cellular processes from proliferation to terminal differentiation offers a promising approach toward preventing cancer progression. Over the past year we have begun to study differentiation in non-small cell lung cancer cell lines by three different approaches: 1) Evaluating the function and regulation of known differentiation antigens such as the Clara cell protein CC10. Analysis of CC10 mRNA expression reveals that the tumor promoter TPA and serum stimulation induce expression of CC10 in the H1334 cell line but not in H1299, both of which express CC10 by in situ hybridization. This is in spite of similarly high basal levels of jun and fos oncogenes (mediators of the TPA signal) and similar patterns of induction of these oncogenes by TPA and serum. Further studies using other biologically relevant agents and analysis using a human CC10 promoter-CAT construct are underway to clarify this and to determine the significance of altered CC10 expression to progressive pulmonary neoplasia. 2) Developing model systems of differentiation to enable the study of molecular mechanisms of differentiation control in lung carcinogenesis. We have previously demonstrated that TPA induced macrophage differentiation correlates strongly with c~jun expression. Our data in lung cancer shows that TPA does not have a similar effect (no growth cessation), perhaps because the induction of jun/fos is much lesser in magnitude and of shorter duration. We are currently also evaluating other potential differentiating agents such as the Na+/K+ ATPase inhibitor bufalin, signal transduction pathway inhibitors, and cytokines. 3) Using immunohistochemistry and flow cytometry to study differentiation markers and genes controlling differentiation and proliferation in primary lung tumors and premalignant lesions to identify targets for early detection screening. We have developed a technique for jun immunostaining and preliminary data shows that jun is highly expressed in primary lung tumors as well as in 5/6 cell lines. This will be correlated with fos, "downstream" genes (CD44, vimentin), prognosis in advanced cancer, and expression in premalignant lesions. These studies will shed light on the biology of lung cancer and enable us to identify targets for early detection and intervention as well as potentially develop strategies for enforcing terminal differentiation as a therapeutic goal during lung carcinogenesis.